Basidium fungi (Basidiomycetes) include totals of thousands of species. They form a group that include many edible mushrooms. They are the most well-known basidium fungi. The group includes most of the mushrooms. All have a single celled basidium that produces four basidiospores. Their fruiting bodies on which basidia form are often large and conspicuous.
Reproduction in basidium fungi is complex especially among the rusts and smuts. Several types of asexual spores are produced and during the life cycle phase, basidiomycetes produce basidiospores following sexual reproduction. Basidiospores are borne on club-shaped structures called basidia. Each of these usually produce four spores. Their color makes an important characteristic used by experts to identify certain species of mushrooms.

Edible varities of Basidiomycetes are companions of lethal species. The group Amanita phalloides accounts for about 90 percent of all deaths caused by mushroom poisoning. Some groups such as Boletus and Russula contain both edible and poison species. Another example is the Puffball in the genus Scleroderma which are poisonous, though for many puffballs are a source of food.

The U.S. Public Health Service has stated, "Wild mushrooms should not be used for food unless their identity and lack of toxicity have been established beyond a shadow of a doubt."